Wireless communication apparatus and wireless communication method

ABSTRACT

A wireless communication apparatus is capable of improving communication efficiency by reducing the amount of control information transmitted. A channel quality information extraction section extracts CQI&#39;s from a received signal. An allocation control section allocates subcarriers for every communication terminal apparatus and selects a modulation scheme in such a manner that required transmission rate is satisfied for each communication terminal apparatus based on required transmission rate information, etc. and CQI&#39;s for communication terminal apparatus of each user. A required subcarrier number determining section decides the number of subcarriers allocated to every communication terminal apparatus so as to satisfy the required transmission rate for each communication terminal apparatus. A required subcarrier number information generating section generates information for the number of subcarriers allocated to every communication terminal apparatus. A subcarrier allocation section allocates packet data to selected subcarriers. Modulating sections adaptively modulate packet data allocated to each subcarrier.

CROSS-REFERENCE(S) TO RELATED APPLICATION(S)

This is a continuation of U.S. application Ser. No. 13/461,527 filed May1, 2012, which is a continuation of U.S. application Ser. No. 12/391,787filed Feb. 24, 2009 (now U.S. Pat. No. 8,223,691), which is acontinuation of U.S. application Ser. No. 10/568,673 filed Apr. 7, 2006(now U.S. Pat. No. 7,522,544), which is a U.S. National Stage under 35USC 371 of PCT/JP2004/012311 filed Aug. 20, 2004, which is based on JP2003-295972 filed Aug. 20, 2003, the entire contents of each of whichare incorporated by reference herein.

BACKGROUND

1. Technical Field

The present invention relates to a wireless communication apparatus andsubcarrier allocation method. More particularly, the present inventionrelates to a wireless communication method and subcarrier allocationmethod combining adaptive modulation and frequency scheduling.

2. Description of the Related Art

A multi-user adaptive modulation OFDM system is a system for carryingout effective scheduling for an entire system according to a propagationpath of each mobile station. Specifically, a base station apparatus isconstituted by a system for allocating a plurality of subcarriersappropriate for each user based on channel quality (frequency divisionuser multiplexing), and selecting appropriate modulation coding schemes(hereinafter referred to as “MCS”) for each subcarrier. Namely, a basestation apparatus is capable of carrying out multi-user high-speed datacommunication by allocating subcarriers in a manner that is the mosteffective utilization of frequency capable of satisfying thecommunication quality (for example, minimum transmission rate, errorrate) desired by each user based on channel quality, selecting MCS toensure maximum throughput for each subcarrier, and carrying out datatransmission. In this way, in a multi-user adaptive modulation OFDMsystem such as, for example, “MC-CDM Method Using Frequency Scheduling,”Technical Report of the Institute of Electronics Information andCommunication Engineers of Japan, RCS2002-129, July 2002, pp. 61-pp.66), a reporting method for reporting channel quality information fromeach mobile station to a base station apparatus is proposed.

An MCS selection table decided in advance is used in the selection ofMCS. An MCS selection table shows correspondence between receptionquality such as CIR (Carrier to Interference Ratio) etc. and error ratessuch as packet error rate (hereinafter referred to as “PER”) or biterror rate (hereinafter referred to as “BER”) etc. for each MCSmodulation scheme and error encoding scheme. An MCS of a maximum speedcapable of satisfying the desired error rate is then selected based onmeasured reception quality in MCS selection.

However, in the related art, in frequency division user multiplexing,each mobile station reports channel quality information for allsubcarriers to a base station apparatus. FIG. 1 shows a reporting formatof signal to noise ratio (hereinafter referred to as “SNR”) of channelquality information reported from a mobile station to a base stationapparatus of the related art, and FIG. 2 is a view showing arelationship between SNR report bits and modulation scheme. As shown inFIG. 1, the base station apparatus allocates subcarriers and performsadaptive modulation by receiving notification of SNR report bits forevery subcarrier in subcarrier order from each communication terminalapparatus for all subcarriers in the communication band. In this event,in the case that transmission by 64 QAM adopted as a modulation schemesatisfying the desired transmission rate and PER is required, the basestation apparatus selects the first or fifth subcarrier for which an SNRreport bit is 3, and allocates packet data employing 64 QAM to the firstor fifth subcarrier.

However, with the base station apparatus and subcarrier allocationmethod of the related art, each mobile station reports channel qualityinformation for all subcarriers to the base station apparatus,regardless of whether only some of the subcarriers of all of thesubcarriers within the communication band are used. The amount ofchannel quality control information therefore becomes extremely large inaccompaniment with increase in the number of mobile stations and numberof subcarriers, and communication efficiency therefore falls.

BRIEF SUMMARY

It is therefore an object of the present invention to provide a wirelesscommunication apparatus and subcarrier allocation method capable ofimproving communication efficiency by reducing the amount of controlinformation transmitted.

According to a first aspect of the present invention, a wirelesscommunication apparatus is comprised of a subcarrier number determiningsection determining a number of subcarriers, of all subcarriers within acommunication band, to be allocated to each communicating party in sucha manner as to achieve transmission rates required by each communicatingparty, a first transmission section transmitting a number of subcarriersdetermined by the subcarrier number determining section to eachcommunicating party, and an allocation control section selectingsubcarriers allocated with packet data for every communicating partybased on required transmission rate information for each communicatingparty and channel quality information for the number of subcarriers foreach communicating party extracted from a received signal.

According to a further aspect of the present invention, communicationterminal apparatus comprises a subcarrier selection sectioncommunicating with the wireless communication apparatus and selectingsubcarriers of the number of subcarriers using information for thenumber of subcarriers extracted from the received signal in order ofgood reception quality, a channel quality information generating sectiongenerating the channel quality information for subcarriers selected atthe subcarrier selection section, and a second transmission sectiontransmitting the channel quality information generated by the channelquality information generating section.

According to a still further aspect of the present invention, basestation apparatus is provided with the wireless communication apparatus.

According to a yet further aspect of the present invention, a subcarrierallocation method comprises the steps of determining a number ofsubcarriers, of all subcarriers within a communication band, to beallocated to each communicating party in such a manner as to achievetransmission rates required by each communicating party, transmittinginformation for a determined number of subcarriers to each communicatingparty, and selecting subcarriers allocated with packet data for everycommunicating party based on required transmission rate information foreach communicating party and channel quality information for the numberof subcarriers for each communicating party extracted from the receivedsignal.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a view showing an SNR reporting format of the related art;

FIG. 2 is a view showing a relationship between SNR report bits andmodulation scheme;

FIG. 3 is a block diagram showing a configuration for a wirelesscommunication apparatus of a first embodiment of the present invention;

FIG. 4 is a block diagram showing a configuration for a communicationterminal apparatus of the first embodiment of the present invention;

FIG. 5 is a flowchart showing a method of allocating subcarriers of thefirst embodiment of the present invention;

FIG. 6 is a view showing an SNR reporting format for the firstembodiment of the present invention;

FIG. 7 is a block diagram showing a configuration for a wirelesscommunication apparatus of a second embodiment of the present invention;and

FIG. 8 is a flowchart showing a method of allocating subcarriers of thesecond embodiment of the present invention.

DETAILED DESCRIPTION

The following is a detailed description with reference to the drawingsof preferred embodiments of the present invention.

First Embodiment

FIG. 3 is a block diagram showing a configuration for wirelesscommunication apparatus 100 of a first embodiment of the presentinvention.

RF receiving section 102 down-converts etc. a received signal receivedby antenna 101 from a radio frequency to a baseband frequency for outputto channel quality information extraction section 103.

Channel quality information extraction section 103 extracts CQI's(Channel Quality Indicators) constituting channel quality informationfrom the received signal input by RF receiving section 102 for output toallocation control section 104. Further, channel quality informationextraction section 103 extracts subcarrier identification informationindicating subcarriers selected by each communication terminal apparatusfrom the received signal for output to allocation control section 104.

Allocation control section 104 allocates some of the subcarriers fromwithin all of the subcarriers within a predetermined communication bandto CQI's inputted by channel quality information extraction section 103and transmission information inputted to each communication terminalapparatus from user information accumulation section 106 describedlater, and selects modulation schemes for allocated subcarriers forevery subcarrier. Namely, allocation control section 104 selectssubcarriers and modulation schemes in such a manner as to achieve therequired transmission rate or more for each communication terminalapparatus and carries out allocation of subcarriers and modulationschemes to each communication terminal apparatus in such a manner as togive less than a predetermined PER value for every subcarrier.Allocation control section 104 then outputs allocated subcarrierallocation information to subcarrier allocation section 110 and outputsmodulation scheme information for the selected modulation scheme tomodulation sections 111-1 to 111-N. Required subcarrier numberdetermining section 105 constituting a section for determining thenumber of subcarriers obtains the number of subcarriers that can beallocated to each communication terminal apparatus from user informationfor the communication terminal apparatus of each user inputted by userinformation accumulation section 106.

Namely, required subcarrier number determining section 105 determinesthe number of subcarriers in such a manner as to give the requiredtransmission rate or more at each user communication terminal apparatus.During this time, required subcarrier number determining section 105determines the number of subcarriers while giving a view to maintaininga slight margin with respect to the required transmission rate inanticipation of a drop in reception quality due to fading fluctuation.Further, in the event that the total amount of data for CQI's for theacquired number of subcarriers and subcarrier number information is lessthan the total amount of data for only the CQI's for all of thesubcarriers, the required subcarrier number determining section 105outputs the obtained number of subcarriers to required subcarrier numberinformation generating section 107 as subcarrier number information,and, in the event that the total amount of data for the CQI's and thesubcarrier number information for the obtained number of subcarriers isgreater than the total amount of data for only CQI's for all of thesubcarriers, the total number of subcarriers (for example, 64) withinthe communication band is outputted to the required subcarrier numberinformation generating section 107 as subcarrier number information.

User information accumulation section 106 stores user information forthe required transmission rates and data type, etc., together with datato be transmitted to each communication terminal apparatus and outputsthis to allocation control section 104, required subcarrier numberdetermining section 105 and subcarrier allocation section 110, asnecessary. Here, required transmission rate information is, for example,information about the proportion of the amount of data per unit timerequired by a communication terminal apparatus of one user with respectto the amount of data per unit time required by all communicationterminal apparatus. User information accumulation section 106 can updatethe stored user information by inputting user information from a controlsection (not shown) at a predetermined timing.

Required subcarrier number information generating section 107 outputssubcarrier number information inputted by required subcarrier numberdetermining section 105 to control information multiplexer 109 ascontrol channel information.

Allocation information generating section 108 generates controlinformation constituted by a pair consisting of identificationinformation indicating each subcarrier inputted by allocation controlsection 104 and subcarrier modulation scheme information and outputs thegenerated control information to control information multiplexer 109.

Control information multiplexer 109 multiplexes control information forthe number of subcarriers inputted by the required subcarrier numberinformation generating section 107 and allocation information andmodulation scheme information inputted by allocation informationgenerating section 108 and outputs multiplexed control information toswitching section 112 for every subcarrier. Control informationmultiplexer 109 multiplexes subcarrier number information and allocationinformation, as well as control information other than modulation schemeinformation.

Subcarrier allocation section 110 allocates packet data to communicationterminal apparatus for each user for all of the subcarriers within thecommunication band using allocation information inputted by allocationcontrol section 104 and user information inputted by user informationaccumulation section 106 and outputs packet data allocated to eachsubcarrier to modulation sections 111-1 to 111-N carrying out modulationusing modulation schemes selected for every subcarrier.

Modulation sections 111-1 to 111-N are provided in the same number asthere are subcarriers, and modulate packet data inputted by subcarrierallocation section 110 using a modulation scheme of the modulationscheme information inputted by allocation control section 104 and outputthe result to switching section 112.

Switching section 112 switches control information outputted by controlinformation multiplexer 109 and inputted after modulation by modulators(not shown) and packet data modulated at modulation sections 111-1 to111-N and outputs this information to inverse fast Fourier transform(hereinafter referred to as IFFT) section 113.

IFFT section 113 then subjects control information inputted by switchingsection 112 for every subcarrier or packet data for every subcarrier toIFFT and outputs the result to guard interval (hereinafter referred toas “GI”) insertion section 114.

GI insertion section 114 inserts GI's into control information or packetdata inputted by IFFT section 113 and outputs this to RF transmissionsection 115.

RF transmission section 115 up-converts etc. control information orpacket data inputted from GI insertion section 114 from a basebandfrequency to a radio frequency for transmission to antenna 101.

Next, a description is given of a configuration for communicationterminal apparatus 200 using FIG. 4. FIG. 4 is a block diagram showing aconfiguration for communication terminal apparatus 200.

RF receiving section 202 down-converts a signal received by antenna 201from a radio frequency to a baseband frequency etc., for output to a GIremoval section 203.

GI removal section 203 removes GI's from a received signal inputted fromRF receiving section 202 for output to a fast Fourier transform(hereinafter referred to as “FFT”) section 204.

After a received signal inputted by GI removal section 203 is convertedfrom a serial data format to a parallel data format, FFT section 204despreads each item of data converted to parallel data formed using aspreading code, subjects this to fast Fourier transformation, andoutputs this to equalizer 207, channel estimation section 206 andchannel quality estimation section 205.

Channel quality estimation section 205 estimates channel quality from areceived signal subjected to FFT inputted by FFT section 204 and outputsthe estimation results to subcarrier selecting section 214 and channelquality information forming section 215.

Channel quality estimation section 205 takes, for example, an SIR(Signal to Interferer Ratio) as estimation results. The estimationresults are not limited to SIR, and arbitrary estimation results such asCIR (Carrier to Interferer Ratio), etc., can also be used.

Channel estimation section 206 performs channel estimation using areceived signal subjected to FFT inputted by FFT section 204 and outputsestimation results to equalizer 207.

Equalizer 207 corrects amplitude and phase distortion using estimationresults inputted by channel estimation section 206 for received signalssubjected to FFT inputted by FFT section 204 for output to separatingsection 208.

Separating section 208 separates the received signal input by equalizer207 into a control channel signal and a data channel signal, outputs thecontrol channel signal to control information extraction section 211,and outputs the data channel signal to demodulating sections 209-1 to209-N.

Demodulating sections 209-1 to 209-N subject a received signal inputtedby separating section 208 to adaptive modulation in accordance withmodulation scheme information inputted by allocation informationextraction section 212 for every subcarrier and output the result toparallel/serial (hereinafter abbreviated to “P/S”) converter 210.

P/S converter 210 converts the received signals inputted by decodingsections 209-1 to 209-N from parallel data format to serial data formatto acquire received signal data.

Control information extraction section 211 extracts control informationfrom the received signal inputted by separating section 208 and outputsthis to allocation information extraction section 212 and subcarriernumber information extraction section 213.

Allocation information extraction section 212 extracts modulation schemeinformation and subcarrier number information from control informationinputted by control information extraction section 211 and outputsmodulation scheme information for each subcarrier to correspondingdemodulating section 209-1 to 209-N by referring to the subcarriernumber information.

Subcarrier number information extraction section 213 extracts subcarriernumber information from control information inputted by controlinformation extraction section 211 and outputs this to subcarrierselecting section 214.

Subcarrier selecting section 214 selects subcarriers for the number ofsubcarriers designated by the base station apparatus using subcarriernumber information inputted by subcarrier number information extractionsection 213 in order of good channel quality using SIR measurementresults inputted by channel quality estimation section 205. Subcarrierselecting section 214 outputs selected subcarrier information to channelquality information forming section 215.

Channel quality information forming section 215 constituting a channelquality information generating section has a reference table storingchannel quality selection information associating SIR's and CQI's, andselects CQI's by referring to channel quality selection informationemploying SIR inputted by channel quality estimation section 205 foreach subcarrier selected using subcarrier information inputted bysubcarrier selecting section 214. Channel quality information formingsection 215 outputs CQI's to RF transmission section 216 for everyselected subcarrier.

RF transmission section 216 up-converts etc. a transmission signalcontaining CQI's inputted by channel quality information forming section215 from a baseband frequency to a radio frequency and transmits this toantenna 201.

Next, a description is given of a subcarrier allocation method usingFIG. 5. FIG. 5 is a flowchart showing a method for allocatingsubcarriers.

First, required subcarrier number determining section 105 determines thesubcarrier number S_(k) (where k is a user number and is an arbitrarynatural number of two or more) allocated to each communication terminalapparatus 200 using the user information (step ST301).

Required subcarrier number determining section 105 obtains thesubcarrier number S_(k) from the following equation (1) or (2).

S _(k) =┌α×R _(k) /r┐  (1)

where S_(k): subcarrier number (where k is a user number that is anatural number of 2 or more),

α: constant,

R_(k): required transmission rate of communication terminal apparatus200-k (where k is user number and is a natural number of 2 or more),

r: transmission rate for one subcarrier while employing modulationcoding schemes having a highest transmission rate or having atransmission rate for one subcarrier while using modulation codingschemes satisfying a required packet error rate using a channel qualityvalue of a value that is a sum of average signal to noise ratio and aconstant γ (for example, a constant of γ=0 to 3 dB); and ┌α×R_(k)/r┐:integer larger than (α×R_(k)/r).

S _(k)=┌(β×R _(k) ×N)/(R ₁ +R ₂ + . . . +R _(k))┐  (2)

where S_(k): subcarrier number (where k is a user number that is anatural number of 2 or more),

β: constant (for example, (β=2.0 to 4.0),

R_(k): required transmission rate of communication terminal apparatus200-k (where k is user number and is a natural number of 2 or more),

N: the total number of subcarriers, and

┌(β×R_(k)×N)/(R₁+R₂+ . . . +R_(k))┐: integer larger than

((β×R_(k)×N)/(R₁+R₂+ . . . R_(k)))

Equation (1) is for determining the number of subcarriers by using therequired transmission rate for each communication terminal apparatus andthe modulation scheme and encoding rates for which transmission rate isa maximum, or determining the number of subcarriers by using therequired transmission rate for each communication terminal apparatus anda transmission rate per subcarrier when using a modulation scheme andencoding rate satisfying the desired error rate for the averagereception quality of each communication terminal apparatus. Further,equation (2) is for determining the number of subcarriers using theratio of the number of all subcarriers within the frequency band and therequired transmission rate for each communication terminal apparatus,and the total of the required transmission rate for all communicatingparties.

Next, required subcarrier number determining section 105 calculates thetotal amount of data for the CQI's and subcarrier number information forthe selected subcarriers for each communication terminal apparatus 200and determines whether or not the total amount of data for the CQI's andsubcarrier number information for the selected subcarriers is largerthan the total amount of data for CQI's for all subcarriers (forexample, 64 subcarriers) within a predetermined communication band (stepST302). Namely, required subcarrier number determining section 105determines whether or not equation (3) is satisfied.

Sk>(Q×N)/(Q+log₂N)  (3)

Here, Q: encoding bit number required for quantizing SNR information;and

N: total number of subcarriers.

In the event that the total amount of data for the selected subcarrierCQI's and subcarrier number information is not larger than the totalamount of data for CQI's for all of the subcarriers within apredetermined communication band (i.e., when equation (3) is notsatisfied), required subcarrier number determining section 105determines the subcarrier number S_(k) as the subcarrier numberinformation to be sent to communication terminal apparatus 200-k.Required subcarrier number information generating section 107 thengenerates the subcarrier number S_(k) as subcarrier number informationand transmits and reports the subcarrier number information tocommunication terminal apparatus 200-k (step ST303).

Next, communication terminal apparatus 200-k that received thesubcarrier number information extracts subcarrier number informationfrom the received signal at the subcarrier number information extractionsection 213, and S_(k) subcarriers are then selected at the channelquality information forming section 215 in order of good receptionquality (step ST304).

On the other hand, in step ST302, in the event that the total amount ofdata for the selected subcarrier CQI's and subcarrier number informationis larger than the total amount of data for CQI's for all of thesubcarriers within a predetermined communication band (i.e. equation (3)is satisfied), required subcarrier number determining section 105determines to have CQI's transmitted from communication terminalapparatus 200-k for all of the subcarriers and determines to select thenumber of all the subcarriers. Required subcarrier number informationgenerating section 107 then generates subcarrier number informationselecting all of the subcarriers, and this subcarrier number informationis reported to communication terminal apparatus 200-k (step ST305).

Next, channel quality information forming section 215 of communicationterminal apparatus 200 generates CQI's for each selected subcarrier orfor all of the subcarriers (step ST306).

After this, communication terminal apparatus 200 sends generated CQI'sand subcarrier number information generated by the CQI's in the SNRreporting format shown in FIG. 6, to wireless communication apparatus100 (step ST307). FIG. 6 shows SNR report bits and subcarrier numberinformation for two subcarriers. As shown in FIG. 6, the SNR report bitis “3” and the subcarrier number information is “0” for the firstsubcarrier, and the SNR report bit is “3” and subcarrier numberinformation is “4” for the second subcarrier.

Next, CQI's are extracted from the received signal at channel qualityinformation extraction section 103 of wireless communication apparatus100 and subcarriers are allocated to communication terminal apparatus200-k at allocation control section 104 (step ST308).

According to the first embodiment, the base station apparatus determinesthe number of subcarriers allocated every communication terminalapparatus based on required transmission rate of each communicationterminal apparatus and transmits the determined subcarrier numberinformation to communication terminal apparatus. This means that thecommunication terminal apparatus only has to generate and transmit CQI'sfor the number of subcarriers allocated by the base station apparatus.As a result, it is possible to reduce the amount of control informationand improve communication efficiency.

Moreover, according to the first embodiment, in the event that the totalamount of data for CQI's and subcarrier number information for thenumber of subcarriers allocated to the communication terminal apparatusof each user is larger than the total amount of data for CQI's for allof the subcarriers, the base station apparatus only has to transmitCQI's for all of the subcarriers to the communication terminalapparatus. This means that amount of data transmitted to the uplink canbe reduced by that proportion of subcarrier number information that thecommunication terminal apparatus does not transmit.

Moreover, according to the first embodiment, the communication terminalapparatus selects a number of subcarriers designated by base stationapparatus using subcarrier number information in order of good channelquality and reports this to the base station apparatus. It is thereforepossible to obtain a user diversity effect as a result of it beingpossible for the base station apparatus to allocate packet data tosubcarriers of good reception quality, the throughput of the system as awhole can be improved, and frequency utilization efficiency can beimproved.

Second Embodiment

FIG. 7 is a block diagram showing a configuration for wirelesscommunication apparatus 500 of a second embodiment of the presentinvention. In FIG. 7, portions with the same configuration as for FIG. 3are given the same numerals and are not described. Further, theconfiguration of the communication terminal apparatus is the same as theconfiguration of FIG. 4 and is therefore not described.

Allocation control section 104 allocates subcarriers to communicationterminal apparatus of each user using CQI's inputted by channel qualityinformation extraction section 103 and user information forcommunication terminal apparatus of each user inputted by userinformation accumulation section 106. Allocation control section 104then outputs allocated subcarrier allocation information to subcarrierallocation section 110 and outputs modulation scheme information for theselected modulation scheme to modulation sections 111-1 to 111-N.Allocation control section 104 carries out allocation of subcarriers andmodulation schemes to each communicating party so as to achieve lessthan a predetermined PER value for every subcarrier. Allocation controlsection 104 outputs subcarrier number information at communicationterminal apparatus of each user allocated with actual packet data torequired subcarrier number determining section 105 in frame units.

Required subcarrier number determining section 105 determines the numberof subcarriers for the communication terminal apparatus for which asubcarrier is allocated for one frame previous to the current frameusing subcarrier number information actually allocated at allocationcontrol section 104 inputted by allocation control section 104, andoutputs the determined subcarrier number information to requiredsubcarrier number information generating section 107. On the other hand,for communication terminal apparatus to which subcarriers are notallocated in one frame previous to the current frame, requiredsubcarrier number determining section 105 determines the number ofsubcarriers that can be allocated from user information for eachcommunication terminal apparatus inputted by user informationaccumulation section 106 and outputs the determined subcarrier numberinformation to required subcarrier number information generating section107.

Next, a description is given of a subcarrier allocation method usingFIG. 8. FIG. 8 is a flowchart showing a method for allocatingsubcarriers.

First, allocation control section 104 determines whether or not asubcarrier is allocated to the immediately preceding frame one frameprevious to the current frame (step ST601).

In the event that a subcarrier is allocated to the immediately precedingframe, subcarrier number S_(k)(t) is determined for subcarrier numberinformation transmitted at the current frame from equation (4) (stepST602).

S _(k)(t)=δ×S′ _(k)(t−1)  (4)

Here, S_(k)(t): number of subcarriers of the current frame,

S′k(t−1): the number of subcarriers actually allocated to communicationterminal apparatus 200-k one frame previous to the current frame, and

δ: constant (where 2.0□δ).

In the event where the communication terminal apparatus has stopped orthe amount of movement of the communication terminal apparatus is small,it is possible to determine the number of subcarriers using equation (4)on the side of the communication terminal apparatus as a result of itbeing possible to estimate that fluctuation in channel quality will beslight.

On the other hand, in step ST601, in the event that a subcarrier is notallocated to the immediately preceding frame, subcarrier number S_(k)(t)is determined for subcarrier number information transmitted at thecurrent frame from equation (1) or equation (2) (step ST603).

Next, required subcarrier number information generating section 107generates the subcarrier number S_(k)(t) as subcarrier numberinformation and reports the subcarrier number information tocommunication terminal apparatus 200-k (step ST604).

After this, communication terminal apparatus 200-k that received thesubcarrier number information extracts subcarrier number informationfrom the received signal at the subcarrier number information extractionsection 213, and S_(k) subcarriers are then selected at the channelquality information forming section 215 in order of good receptionquality (step ST605).

Next, channel quality information forming section 215 of communicationterminal apparatus 200 generates CQI's for each selected subcarrier orfor all of the subcarriers (step ST606).

After this, communication terminal apparatus 200 sends generated CQI'sand subcarrier number information generated by the CQI's in the SNRreporting format shown in FIG. 6 to wireless communication apparatus 500(step ST607).

Next, CQI's are extracted from the received signal at channel qualityinformation extraction section 103 of wireless communication apparatus500 and subcarriers are allocated to communication terminal apparatus200-k at allocation control section 104 (step ST608).

According to the second embodiment, the base station apparatusdetermines the number of subcarriers allocated every communicationterminal apparatus of each user based on required transmission rate ofeach communication terminal apparatus and transmits the determinedsubcarrier number information to communication terminal apparatus. Thismeans that the communication terminal apparatus has only to generate andtransmit CQI's for the number of subcarriers allocated by the basestation apparatus. As a result, it is possible to reduce the amount ofcontrol information and improve communication efficiency.

According to the second embodiment, the base station apparatusdetermines the number of subcarriers using a straightforward method ofsimply multiplying the number of subcarriers for one frame previous tothe current frame with a constant. It is therefore possible to implementstraightforward processing for allocating subcarriers and achievehigh-speeds in cases where the speed of movement of communicationterminal apparatus is slow or in cases where communication terminalapparatus have stopped.

Moreover, according to the second embodiment, the communication terminalapparatus selects a number of subcarriers designated by base stationapparatus using subcarrier information in order of good channel qualityand reports the base station apparatus. It is therefore possible toobtain a user diversity effect as a result of it being possible for thebase station apparatus to allocate packet data to subcarriers of goodreception quality and to effectively improve the throughput of thesystem as a whole.

In the first and second embodiments, CQI's are adopted as channelquality information but this is by no means limiting and arbitraryinformation other than CQI's may also be used. Further, wirelesscommunication apparatus 100 of the first embodiment and wirelesscommunication apparatus 500 of the second embodiment are applicable tobase station apparatus.

Each function block employed in the description of each of theaforementioned embodiments may typically be implemented as an LSIconstituted by an integrated circuit. These may be individual chips orpartially or totally contained on a single chip.

“LSI” is adopted here but this may also be referred to as “IC”, “systemLSI”, “super LSI”, or “ultra LSI” depending on differing extents ofintegration.

Further, the method of circuit integration is not limited to LSI's, andimplementation using dedicated circuitry or general purpose processorsis also possible. After LSI manufacture, utilization of an FPGA (FieldProgrammable Gate Array) or a reconfigurable processor where connectionsand settings of circuit cells within an LSI can be reconfigured is alsopossible.

Further, if integrated circuit technology comes out to replace LSI's asa result of the advancement of semiconductor technology or a derivativeother technology, it is naturally also possible to carry out functionblock integration using this technology. Application in biotechnology isalso possible.

This specification is based on Japanese patent applicationNo.2003-295972, filed on Aug. 20, 2003, the entire content of which isincorporated herein by reference.

INDUSTRIAL APPLICABILITY

The base station apparatus and subcarrier allocation method of thepresent invention reduce the amount of control information transmittedand as such are effective in improving communication efficiency, and aretherefore useful in allocation of subcarriers.

What is claimed is:
 1. A base station for receiving a channel qualityindicator from a mobile station, comprising: a determining unitconfigured to perform a determination of whether a mobile station is totransmit (i) first information indicating positions of subcarriersselected by the mobile station within a communication band and secondinformation related with channel qualities of the subcarriers selectedby the mobile station within the communication band, or (ii) channelquality indicators related with all subcarriers within the communicationband without information indicating positions of any of the subcarrierswithin the communication band, wherein a data volume of summation of thefirst information and the second information to be transmitted in (i) issmaller than a data volume of the channel quality indicators relatedwith all subcarriers within the communication band to be transmitted in(ii); a transmitting unit configured to transmit information designatingthe determination of the determining unit and information related with anumber indicating a quantity of the subcarriers to be selected by themobile station, to the mobile station; a receiving unit configured toreceive (i) the first information and the second information or (ii) thechannel quality indicators of all subcarriers within the communicationband, from the mobile station; and an extracting unit configured toextract (i) the received first information and the received secondinformation or (ii) the received channel quality indicators of allsubcarriers within the communication band.
 2. A receiving method forreceiving a channel quality indicator from a mobile station, comprising:performing a determination of whether a mobile station is to transmit(i) first information indicating positions of subcarriers selected bythe mobile station within a communication band and second informationrelated with channel qualities of the subcarriers selected by the mobilestation within the communication band, or (ii) channel qualityindicators related with all subcarriers within the communication bandwithout information indicating positions of any of the subcarrierswithin the communication band, wherein a data volume of summation of thefirst information and the second information to be transmitted in (i) issmaller than a data volume of the channel quality indicators relatedwith all sub carriers within the communication band; transmitting, tothe mobile station, information designating said determination andinformation related with a number indicating a quantity of thesubcarriers to be selected by the mobile station; receiving the firstinformation and the second information in case of (i), or the channelquality indicators of all subcarriers within a communication band incase of (ii), from the mobile station; and extracting (i) the receivedfirst information and the received second information or (ii) thereceived channel quality indicators of all subcarriers within thecommunication band.